Of Interest: This NAC image, taken about 85 minutes after MESSENGERís closest approach during the missionís second Mercury flyby, shows a view of Astrolabe Rupes, named for the ship of the French explorer Jules Dumont díUrville. Rupes is the Latin word for cliff. Mercuryís day/night transition (the terminator) is located on the left side of the image, and the Sun is striking the cliff face of Astrolabe Rupes in the upper right of the image. Also visible in the image are additional unnamed rupes, whose cliff faces are casting dark shadows. One of these rupes intersects the crater Ghiberti, named for the Italian Renaissance sculptor. Rupes on Mercury are thought to have formed as the interior of Mercury cooled and the planet consequently contracted slightly. Determining the number and extent of rupes on Mercury can thus be used to understand the thermal history of the planet.